The demands on automobiles for better fuel economy have been increasing in recent years as concern with environmental issues has been rising. Good fuel economy is also being required of the rubber compositions used for automotive tires. For example, rubber compositions containing a conjugated diene polymer (e.g., polybutadiene, butadiene-styrene copolymer) and a filler (e.g., carbon black, silica) are used for the rubber compositions for automotive tires.
Patent Literature 1, for example, proposes a method for enhancing the fuel economy. This method uses a diene rubber (modified rubber) that has been modified with an organosilicon compound containing an amino group and an alkoxy group. However, the use of the modified rubber may excessively increase the Mooney viscosity and thereby reduce the processability. Meanwhile, wet-grip performance and abrasion resistance are also properties required of the rubber compositions for automotive tires; however, these properties generally assume an inverse relationship with the fuel economy. Thus, a method has been demanded that can enhance the fuel economy, wet-grip performance, abrasion resistance, and processability to high levels in a balanced manner.
Patent Literature 2 proposes a method for enhancing the processability, fuel economy and the like by use of a specific silane coupling agent containing a mercapto group. However, this method still needs to be improved to enhance the fuel economy, wet-grip performance, abrasion resistance, and processability in a balanced manner.